In the harvesting of crops it is desired that the grain be separated from other elements or portions of the crop, such as from pod or cob fragments, straw, stalks, and the like. Agricultural combines typically have employed a rotary threshing or separating system for separating and segregating the grain from such other crop elements or portions. In general, rotary threshing or separating systems are so designed that, as threshing occurs, the resulting crop material is typically caused to fall or be conveyed to a clean grain and tailings conveying system, sometimes also referred to as a collecting and conveying system, or even more simply as a conveying system, for further processing, which processing typically includes the feeding of such resulting crop material from the rotary threshing or separating system onto an underlying vibratory cleaning system or onto one or more conveyors for conveyance to such a cleaning system.
The cleaning system typically includes a set of stacked sieves or shoes that are reciprocally moved, usually in the fore and aft directions, to separate or sift the grain from tailings and material other than grain (MOG). With many combines, as the grain is cleaned from the MOG, it falls through the sieves and drops onto or into one or more underlying clean grain pans that are disposed below the sieves, which pans feed the clean grain to an intersecting, cross, generally laterally extending, clean grain conveyance trough, sometimes referred to as the clean grain auger trough or, more simply, the clean grain trough.
The laterally extending clean grain conveyance trough receives the clean grain conveyed thereto from the clean grain collecting troughs and typically has associated therewith a conveyance mechanism, often in the form of an auger extending therethrough, for moving and delivering the clean grain in such clean grain conveyance trough to an elevator that carries the clean grain up to a clean grain tank.
During the vibration of the sieves, air is blown upwardly and rearwardly through the sieves to carry lighter elements of the MOG, or chaff, away. The heavier elements and tailings that are too large to fall through the sieves and too heavy to be blown away are caused to be moved by the vibrations, generally rearwardly along the top surfaces of the sieves, towards and over rear edges of the sieves to fall onto a tailings pan located below and extending somewhat beyond such rear edges. The tailings pan, similarly to the clean grain pan, feeds the tailings to an intersecting, cross, generally laterally extending, tailings conveyance trough, sometimes referred to as the tailings auger trough or, more simply, the tailings trough.
The sidewardly extending tailings conveyance trough receives the tailings conveyed thereto from the tailings collecting pan and/or troughs and has a conveyance mechanism, often in the form of an auger extending therethrough, for moving and delivering the tailings to a tailings return conveyor operable for carrying the tailings upwardly, back to the cleaning or separating system of the combine, for reprocessing, including further threshing of the tailings.
Over the years, fans of various types, including, by way of example, vane-type fans, paddle fans, and cross-flow fans of various designs, all of which are capable of producing air to be blown upwardly and rearwardly through the sieves to carry the chaff away from the grain and tailings deposited onto the cleaning system sieves, have been employed in or with agricultural combines to provide the desired air flow. Such chaff is typically blown into an optional chaff spreader, operable for distributing the chaff over a desired swath of the field from which the crop is cut, or directed into an optional chopper, operable for mixing the chaff with straw for chopping and distributing such mix, or simply directed downwardly onto the field through a rear opening of the combine.
While all of such noted fan types can operate to produce air flows for carrying chaff away, some fan types have proven more effective at producing the air flow volume desired. Ideally, the fan employed will be able to develop a maximal air flow volume at as low a fan speed as possible. For a number of years now, transverse or cross-flow fans of various designs have been recognized to be particularly well-suited for the noted purpose.
Transverse or cross-flow fan assemblies are well known in the art, and such fan assemblies typically have included axially spaced disk-like members that support a plurality of elongated fan blades in some form of cylindrical pattern or array, often with as many as thirty-six fan blades disposed in a cylindrical arrangement about the axis of rotation of the fan. With some fan assemblies, straight and cross-sectionally curved fan blades have been disposed with the tips of the blades extending generally parallel to the axis of rotation, which fan blade configurations are generally hereinafter referred to as axially aligned fan blade arrangements. In more recent years, newer types of transverse fan assemblies have been developed in which the fan blades in a number of fan assemblies have, instead, been angled, such as in a chevron blade arrangement. Examples of two transverse fan assemblies that have been advantageously employed in combines is found in U.S. Pat. No. 5,599,162, with one disclosed fan assembly utilizing an axially aligned fan blade arrangement and another disclosed fan assembly utilizing a chevron blade arrangement, in both of which assemblies the fan blades have an arcuate cross-section.
Transverse fans have proven particularly useful in combine cleaning systems because such fans can produce a wide stream of air that can be directed upwardly toward the cleaning sieves of the combine cleaning systems but require relatively little space. Such fans, in typical agricultural combines, are disposed such that their air outputs are below the sieves of the cleaning system, and, so, are positioned close to the ground over which the combine moves.
As will be appreciated, rocks and other debris commonly found in fields can be detrimental to the normal high speed rotational operation of fan blades, and broken and/or bent fan blades can affect fan performance, and consequently, the overall efficiency of a combine in which a transverse fan assembly is installed. Accordingly, when transverse fan assemblies are employed with typical combines, the fan blades are normally protected by installing the fan within a fan wrapper or air plenum, with the fan being rotatably mounted within an inner chamber of the air plenum to operably drive air between an air inlet and an air outlet.
Desirably, such transverse fans, especially as employed in combines, will thus provide a relatively wide output of air, and will do so in such a way that they carry sufficient pressure so that, when material is deposited onto the sieves of the cleaning system, they will continue to operate to produce an air flow directed towards the sieves that is adequate for the intended purposes. As noted previously, ideally, such a fan will operate at as low a speed as possible to develop the desired air flow. To some extent, increased air flow can be effected by increasing the rotational speed of the fan, but such an increase in rotational speed is not without consequences, including, generally, increased noise and wear and tear on the fan.
Consequently, users have continued to seek improved fan constructions in which better air flow can be developed while they operate at low speeds.
Although transverse fans have been employed for many years, due to the complex nature of air flow within transverse fan constructions and difficulties in predicting and determining what the consequences of various changes in the design and operation of such transverse fans may be, development of improved fan constructions has proved problemsome.
In general, as transverse fans operate, a relatively large vortex, sometimes referred to as a steering vortex, is formed, generally situated partially within and partially outside of the fan rotor or impeller, near a fan cut-off, which is sometimes referred to as a stabilizer. The position, size, and intensity of such steering vortex is strongly influenced by the structural features of the fan, including the geometric parameters thereof, as well as the volume rate and pressure rate of the fan. Additional, or secondary, vortices may also be produced in the inlet and outlet zones of the fan, and the shape of the air plenum surrounding the fan rotor can greatly influence the performance characteristics of the fan.
In efforts to develop an improved transverse fan construction, it has been found that changes in the construction and configuration of the fan cut-off, including an inclination of the cut-off relative to passing fan blades, can affect the position of the steering vortex and the performance characteristics of the fan. In particular, it has now been found that, when the present invention is incorporated into a transverse fan of the type that has been employed in recent years in combine harvesters for providing air flow to cleaning systems of such harvesters, the transverse fan can provide a better or increased air flow while still operating at a low rotational speed, thereby resulting in better fan performance without the adverse consequences that would otherwise result as fan speed was required to be increased to secure the increased air flow.